1. Field of the Invention
The present invention relates to magnetic resonance imaging (MRI) technology, and more particularly, to a method and device for correcting distortion in MRI.
2. Description of the Prior Art
Due to the influence of various factors, distortion occurs in the MRI process. By their sources, the distortions which are normally found in MRI can principally be divided into magnetic field related distortion and human body related distortion.
The magnetic field related distortion is mainly attributable to the inhomogeneous magnetic field, especially the geometric distortion induced by inhomogeneity of the primary magnetic field. In the case of a highly inhomogeneous magnetic field existing, many signals may overlap to create geometric distortion. Many factors may cause inhomogeneity of a magnetic field, such as implanted metal devices and metal fixture is in the body of the patient.
Human body related distortions mainly include movement distortion, which is generated due the reason that the patient may lose patience and move his body during the prolonged MRI scanning process. Movement artifact is especially evident among very young or restless patients. If the movement artifact is very serious, the image quality will be inferior and causes adverse effects on diagnosis.
At present, the Periodically Rotated Overlapping ParallEL Lines Enhanced Reconstruction (PROPELLER) technology is widely used for movement correction where radial blades acquire data in a spiral fashion and guide the filling of the whole k-space with data in a unique k-space filling mode. This technology can eliminate movement artifact in the most complicated and difficult conditions to acquire images of excellent quality. The k-space is also referred to as frequency space, the x-coordinate and y-coordinate of which respectively refers to the frequency change in the phase encoding direction and frequency encoding direction.
Although PROPELLER technology can effectively correct the movement distortion, it can not correct the geometric distortion caused by inhomogeneity of the magnetic field or specific magnetization.